1. Field of the Invention
This invention relates to a method for handling threads in spiralling or covering machines, and to a spiralling machine or covering machine using that method.
2. Description of the Related Art
To be able to be used, transported and stored, thread has to be wound on supports, which are of various forms and sizes according to the specification of the machine which is to use it in the next process.
Winding is achieved, using winding machines, by depositing the thread on a rotating cylinder or bobbin, which is in the form either of a simple tube or, preferably, a cylinder provided with flanges at one or both ends to retain the wound thread. Flangeless bobbins are preferably used on machines which unwind the thread without rotating the support on which the thread is wound.
Yarn used for producing certain types of fabric or hosiery of considerable elasticity is produced by covering an elastic thread with a spiral of normally non-elastic thread, which improves its appearance and strength.
This operation is performed by machines known as covering or spiralling machines.
For reasons of clarity and brevity, in the ensuing description only the term "spiralling machine" will be used instead of the two alternative team "spiralling machine" and "covering machine". In these machine a winding of thread in bobbin from is rotated at high speed (up to 25,000 r.p.m. and beyond) on an internally hollow rotary shaft (spindle).
A thread (usually the elastic part of the yarn) runs through the hole in the spindle, travelling longitudinally along the central axis of the bobbin, while the spindle rotates.
At the same time, the thread present on the rotating bobbin unwinds at one end to deposit as a spiral on the central thread. Yarn combinations can be produced from different threads originating from different bobbins, possibly rotating in opposite directions, and wound as a spiral on the central thread.
Currently, for this type of machine cylindrical bobbins are used flanged at one or both ends, with the flange surface perpendicular to bobbin axis or of frusto-conical shape so that the thread section along a plane on which the bobbin axis lies defines a parallelogram.
Although such a winding presents good unwinding speed and good thread retention, it however produces numerous problems both during spiralling and during bobbin preparation.
Firstly, it is totally unsuitable for unwinding the thread with the support at rest.
Moreover, when the thread is unwound from the bobbin for spiralling, it periodically unwinds from turns close to the flange.
As the flange projects outwards from the wound turns, in such cases the force required to unwind the thread is such as to damage and/or break the thread, which is compelled to travel through a large curve before reaching the thread on which it is to be spirally deposited.
This means that the thread slides on the entire remaining part of the winding and on the inner surfaces of the flanges, with the consequent possibility or displacement and overlapping of the turns and relative hold-ups in unwinding in correspondence with the flange situated at the unwinding end, where the thread can remain squashed between the flange and the adjacent turns.
Moreover, when winding the thread onto a flanged bobbin by a winding machine, the operator has to very accurately adjust manually the turn arrangement at the bobbin ends, so as to ensure that no accumulations or shortages are present.
In this respect, a thread arrangement which is not perfectly uniform could prejudice regular thread unwinding during the subsequent spiralling operation.
Finally, even minimum mechanical deformation of a flange (due to possible constructional defects thereof or to impact suffered during use) results in overall unbalance in the rotation of the spindle carrying the bobbin, with consequent reduction in the average life of the mechanical components, such as ball bearings, of the spiralling machine.
An object of the present invention is to indicate a method for handling threads in spiralling machines which obviates the aforesaid drawbacks.
A further object of the present invention is to indicate a method for handling thread in spiralling machines which does not require the use of complicated or particularly costly techniques.
A further object of the present invention is to indicate a method by which the manufacturing and operating costs of spiralling machines can be reduced with respect to the known art.
A further object of the present invention is to provide a spiralling machine which uses the method of the present invention.